The present invention relates to a liquid crystal display panel forming a part of a liquid crystal display device, and more particularly, to a liquid crystal display panel suited for displaying patterns (characters, mark graphics, and so forth) in the shape as required in cloudy white or black, or in the form of a colored pattern against a transparent background.
As liquid crystal display devices, using a liquid crystal display (LCD) panel, have advantages of low-profile shape, light weight, and further, very low power consumption, these devices have come to be used as display devices for a wide variety of equipment including various kinds of portable electronic equipment such as a tabletop calculator, cellular phone, wrist watch, camera, video camera, note-type personal computer, and so forth.
With such a liquid crystal display panel, a pair of transparent substrates are bonded together by a sealing section provided on the periphery of a display region with a given spacing provided therebetween, and a liquid crystal cell is made up by sealing a liquid crystal layer in-between the spacing. By applying a voltage to parts of the liquid crystal layer via signal electrodes and opposite electrodes formed on an opposed inner face of the two substrates, respectively, optical properties (twist of a polarization axis, birefringence, transmission/scattering, and so on) of the liquid crystal layer can be varied.
Accordingly, through a combination of a polarizing film disposed on both sides of the liquid crystal cell or by the use of the liquid crystal cell itself, parts of the liquid crystal layer where a voltage is applied come to differ from parts of the liquid crystal layer where no voltage is applied, in terms of transmission/absorption or scattering of light, or hue of light, thereby enabling a variety of displays to be effected.
Consequently, with this type of liquid crystal display panel, parts where the respective signal electrodes formed on one of the substrates are opposed to (or cross in the case of a dot-matrix type liquid crystal display panel) the respective opposite electrodes formed on the other of the substrates, with the liquid crystal layer interposed therebetween, perform functions of display portions (pixels).
In order to enable each of the display portions (pixels) to be driven independently, it is necessary to provide the periphery of the respective display portions with a gap where no electrode is installed.
For this reason, in the case of a liquid crystal display panel using, for example, twisted nematic (TN) liquid crystal in a liquid crystal layer, it has been possible to effect consistent display across the entire area of a display region in a condition wherein no voltage is applied to the liquid crystal layer, but impossible to do so in a condition wherein a voltage is applied thereto because the voltage cannot be applied to regions of the gaps where no electrode has been installed.
Further, in the case of a liquid crystal display panel for selectively displaying isolated patterns against a background in consistent display, there is a need of forming wiring electrodes for use in applying a voltage to electrodes constituting respective isolated pattern display portions, in such a way as to cross electrodes in a background region while providing a gap between the electrodes and the wiring electrodes. As with the case of the signal electrodes and the opposite electrodes, the wiring electrodes are formed of a transparent ant electrically conductive film, such as an indium tin oxide (ITO) film.
However, if, for effecting display at any of the pattern display portions, a voltage is intended to be applied to a signal electrode and an opposite electrode for the relevant pattern display portion, this will cause a problem that, because the voltage is applied via a wiring at connected to the signal electrode, the voltage will be applied to a portion of the liquid crystal layer between the wiring electrode and the opposite electrode as well, so that a region of the wiring electrode as well as the relevant pattern display portion is turned into a display state.
Accordingly, the wiring electrodes are rendered very thin in width so as to be inconspicuous. However, if the same are rendered too thin, this will increase electrical resistance, causing a problem of poor responsivity in display.
Also, in the case of a liquid crystal display panel for use in a viewfinder of a camera, and the like, it is important from the viewpoint of enhanced visibility from a viewer to have an even display across the entire area of a display region, and to have a transmittance as high as possible, except for necessary patterns such as a target pattern for auto focus, and the like.
In order to attain a high transmittance, a liquid crystal display panel using a liquid crystal layer capable of obtaining a high contrast ratio without use of polarizing films is promising.
For example, a liquid crystal display panel using a scattering-type liquid crystal layer with transparent solids made of organic polymers diffused in liquid crystal is in a milky white state causing incident light to scatter when no voltage is applied to the liquid crystal layer, but is turned into a transparent state having a high transmittance when a voltage is applied thereto.
It follows therefore that for effecting display only at necessary display portions such as a target pattern for auto focus, and the like, against a transparent background, no voltage may be applied to the liquid crystal layer only at display portions to be displayed while a voltage is applied to the entire region of the liquid crystal layer, other than regions of the display portions to be displayed.
However, when no voltage is applied to electrodes at the display portions, no voltage is applied to wiring electrodes connected thereto either, and consequently, no voltage is applied to a portion of the liquid crystal layer interposed between the wiring electrodes and the opposite electrodes, so that the portion of that liquid crystal layer is not turned into a transparent state. Consequently, it follows that the entire region of the liquid crystal layer, other than the regions of the necessary display portions, cannot be rendered transparent.
The present invention has been developed to solve such problems as described in the foregoing, and it is therefore an object of the invention to provide a liquid crystal display panel capable of displaying isolated patterns against a transparent background, wherein a consistently transparent state can be attained with ease across the entire area of a display region, other than regions of necessary pattern display portions, in a condition where a voltage is applied to a liquid crystal layer in a background region.
To attain the object as described above, a liquid crystal display panel according to the present invention is as follows.
A first substrate with signal electrodes formed on a face thereof is bonded to a second substrate with an opposite electrode formed on a face thereof at a given spacing provided by a peripheral sealing section interposed therebetween on the periphery of a display region such that the signal electrodes are opposed the opposite electrode, and a liquid crystal layer is installed in between the spacing.
The signal electrodes include a peripheral electrode formed substantially across the entire area of the display region, pattern electrodes formed in isolation within the peripheral electrode, and wiring electrodes formed across the peripheral electrode with a gap provided between the same and the peripheral electrode for selectively applying a voltage to the respective pattern electrodes.
The opposite electrode is installed over the entire area of the display region in such a way as to oppose the signal electrode.
With the liquid crystal display panel, the first substrate, second substrate, signal electrodes and opposite electrode are all transparent, the liquid crystal layer undergoes changes in optical properties depending on whether or not a voltage is applied between the signal electrodes and the opposite electrode, and a transmittance of portions of the liquid crystal layer, where a voltage is applied, increases.
Further, with the liquid crystal display panel, wiring sealing sections formed of a transparent sealing material are installed in the display region between the wiring electrodes and the opposite electrode such that portions of the display region where the wiring sealing sections are installed always have a transmittance substantially equal to that of portions of the liquid crystal layer where a voltage is applied.
A first substrate with signal electrodes formed on a face thereof is bonded to a second substrate with an opposite electrode formed on a face thereof at a given spacing provided by a peripheral sealing section interposed therebetween on the periphery of a display region such that the signal electrodes are opposed the opposite electrode, and a liquid crystal layer is installed in between the spacing.
The signal electrodes include a peripheral electrode formed substantially across the entire area of the display region, pattern electrodes formed in isolation within the peripheral electrode, and wiring electrodes formed across the peripheral electrode with a gap provided between the same and the peripheral electrode for selectively applying a voltage to the respective pattern electrodes.
According to the present invention, the wiring sealing sections formed of the transparent sealing maternal, instead of the liquid crystal layer, are installed between the wiring electrodes and the opposite electrode, and optical properties of the wiring sealing sections are rendered equal to those of the liquid layer where a voltage has been applied, whereby a transmitted of the portions of the liquid crystal layer in a condition where the voltage has been applied becomes substantially equal to that of the wiring sealing sections, so that quasi-consistent display can be attained across the entire area of the display region.
In the case of using scattering liquid crystal layer composed of mixed liquid crystal comprised of liquid crystal and transparent solids as the liquid crystal layer, with a scattering type liquid crystal layer to which a transparent state occurs by applying a voltage thereto, by installing the wiring sealing sections which are transparent in gaps between the wiring electrodes and the peripheral electrode as well, a substantially uniform transmittance can be obtained with ease over the entire area of the display region as a result of a transparent state of the liquid crystal layer and transparency of the wiring sealing sections, in a condition where a voltage is applied to the liquid crystal layer. Further, by installing a sealing section formed of the same transparent sealing material as a transparent sealing material for the wiring sealing sections in gaps between the respective pattern electrodes and the peripheral electrode as well, a more uniform transmittance can be obtained over the entire area of the display region.
Furthermore, if the wiring sealing sections installed in the display region are isolated by separating the same from the peripheral sealing section installed on the periphery of the display region, thermal contraction and thermal expansion occurring to the periphery of the substrates are first absorbed by the peripheral sealing section even in case that rapid changes in temperature occurs to an application environment of the liquid crystal display panel, and consequently, thermal contraction and thermal expansion propagated to the wiring sealing sections are mitigated.
In particular, in the case of using the scattering type liquid crystal layer for the liquid crystal layer, the structure of the transparent solids is broken down when subjected to rapid changes in temperature, and as a result, there arises a risk that regions where a transparent state does not occur even when a voltage is applied will occur to the periphery of the wiring sealing sections. However, by installing the wiring sealing sections in isolation as described above, thereby mitigating effects of thermal contraction and thermal expansion, it is possible to prevent occurrence of unevenness in display of the liquid crystal layer, thus effectively contributing to implementation of consistent transmissive display over the entire area of the display region.
Further, for the peripheral sealing section, a sealing having high reliability is adopted in order to protect the liquid crystal layer from the application environment of the liquid crystal display panel. However, for the wiring sealing sections for which transparency is particularly important, a material lower in hardness and softer (more elastic) than a material used for the peripheral sealing section, such as a resin not prone to accumulation of stress, is preferably used so as to reduce stress on the liquid crystal layer as much as possible against changes in temperature of the liquid crystal display panel.
Furthermore, in the case of the scattering type liquid crystal layer, the transparent solids are formed in the liquid crystal layer by ultraviolet irradiation, thereby raising a risk of fluidity of liquid crystal being hindered due to adhesion of the transparent solids to the substrates. In such a situation, as compared with the case of liquid crystal being in liquid state, a structure of the transparent solids is susceptible to breakdown due to stress caused by the sealing sections, and once the structure is broken down, such a condition is maintained.
Accordingly, by installing an ultraviolet absorbing layer in regions in the vicinity of the peripheral sealing section and the wiring sealing sections, respectively, it becomes possible to keep the liquid crystal lying around the periphery of the sealing sections in liquid state, and to maintain fluidity thereof through absorption of ultraviolet rays irradiated when forming the transparent solids.
It is possible to employ the pattern electrodes of the signal electrode as target display portions for auto focus, in the shape of a target pattern which are installed in the viewfinder of a camera.
In such a case, if a gap in a range of 30 to 70 xcexcm in width is formed between the respective target (pattern) electrodes and the peripheral electrode, this will allow outlines of the respective target display portions, even in a non-display state, to be dimly visible, serving the convenience of a viewer in recognizing a location thereof beforehand.
Further, at least a part of the peripheral sealing section may be rendered transparent, and a light source for emitting light to the liquid crystal layer from outside of the peripheral sealing section through a transparent part thereof may be installed.
The light source is preferably disposed at a location opposite to a shorter side of the wiring sealing sections, suited for emitting light from outside of the peripheral sealing section. Further, the light source may be a light source for emitting colored light.
Further, a convex lens or a diffusion film, for irradiating the liquid crystal layer in whole with light emitted from the light source, is preferably installed between the light source and the transparent part of the peripheral sealing section.
With the liquid crystal display panel provided with the light source as described above, because a transparent state occurs over the entire area of the display region by applying a voltage to the target electrodes and the peripheral electrode, outgoing light from the light source travels in a straight line through the liquid crystal layer, and is not sent out in a direction along which it is transmitted through the first substrate or the second substrate. By selectively stopping voltage application to the target electrodes, the light from the light source can be sent out in a direction along which it is transmitted through the first substrate or the second substrate due to the scattering property of the part of the liquid crystal layer.
Hereupon, for example, as seen by the viewer from the external side of second substrate, the light source comes out only from the a display portion corresponding to the target electrode to which no voltage is applied, but does not come out from a background region surrounding the display portion, and consequently, this is quite effective resulting from no deterioration of visibility in the case of the viewer seeing given information on the first substrate side of the liquid crystal display panel through the background region while the target pattern is displayed by the target electrode.
The light source is preferably disposed at the location opposite to the shorter side of the wiring sealing sections, suited for emitting light from outside of the peripheral sealing section. By causing the light emitted by the light source to fall on the liquid crystal layer from the peripheral part of the liquid crystal display panel, it is possible to obtain a contrast ratio between the background region displayed by the agency of the peripheral electrode, and the target display portions displayed by the agency of the target electrodes. However, there is a risk of reflection occurring at the boundary between the liquid crystal layer and the wiring sealing sections due to a slight difference in refractive index between the liquid crystal or the organic polymers, in the liquid crystal, and the wiring sealing sections with the result that a portion of the light emitted by the light source can be seen through the wiring sealing sections. For this reason, the light source is preferably disposed at the location as described above in order to obtain evenness in display of the background region.
Further, by taking advantage of scattering properties of the liquid crystal layer at the target display portions, and causing incoming light from the light source to be sent out towards the side of the viewer, it is possible to obtain a contrast ratio between the target display and information visually recognized after transmitted through the background region in a transparent state. However, if the light emitted by the light source is too intense, this will cause the pupil of the eyes of the viewer to dilate, and consequently, the viewer visually recognizes mainly the light emitted by the light source in the case where the contents of the information visually recognized after transmitted through the background region are dark, so that a recognition degree of the information as seen through the background region deteriorates. Accordingly, if visual sensitivity is utilized with the use of a light source emitting colored light, this will enable the viewer to sufficiently recognize the target display portions even though brightness of the light source is subdued.
In such a case, if a light source emitting a plurality of differently colored lights is adopted so as to enable the plurality of the colored lights to be selected, it becomes possible to further enhance visibility of the target display portions because a tone of the colored lights can be selected according to the color of information transmitted through the peripheral display region of the liquid crystal display panel.
Further, in the case of using the scattering type liquid crystal layer composed of liquid crystal and organic polymers mixed therewith as the liquid crystal layer, regions where a structure of organic polymers differs from that in other regions occur to the periphery of the sealing sections due to substantial variation in thermal effect. Accordingly, it is desirable to install an adiabatic sealant in the peripheral region of the first substrate as well as the second substrate of the liquid crystal display panel. By so doing, it becomes possible to prevent a rapid heating or cooling phenomenon from the periphery of the liquid crystal display panel from taking place.
Further, by coloring the adiabatic sealant, it is also possible to prevent the light emitted from the light source from being reflected from the periphery of the liquid display panel. In particular, it is preferable to color the adiabatic sealant so as to render the same to double as a light absorption layer capable of absorbing light in color of the emitted light of the light source. Further, the adiabatic sealant may be colored black, thereby absorbing light at all wavelengths in the visible range.